Polyether polyols can be used in the preparation of polyurethane and polyisocyanurate foams (foams), and are typically prepared from propylene oxide and/or ethylene oxide, using initiators such as sucrose, sorbitol, or glycerol, for example. Polyurethane foams prepared from polyether polyols are used in a variety of applications, including construction, appliance, automotive, and carpet applications. Rigid foams, in particular, are used in appliance and construction applications, for example. A polyol mixture used to prepare polyurethane foam formulations can include a blowing agent, in addition to other components. Blowing agents can be used to create cellular structures within a foam. Some conventional blowing agents, such as halogenated hydrocarbons, for example, can be perceived as harmful to the environment.
Non-halogenated hydrocarbon blowing agents, that is, hydrocarbon blowing agents (HCBAs) are important alternatives to traditional halogenated hydrocarbon blowing agents. Hydrocarbons such as pentane and cyclopentane have been used successfully as blowing agents in polyurethane systems, and are not believed to harm the ozone layer of the atmosphere. The use of hydrocarbons as blowing agents is demonstrated in, for example, U.S. Pat. No. 3,072,582. The use of hydrocarbon blowing agents can present problems, however.
Insolubility of hydrocarbon blowing agents in polymer formulations can lead to processing problems, particularly in producing polyurethane and polyisocyanurate foam products, for example. The possibility of phase separation of HCBAs from a foam formulation makes it necessary to take measures to maintain a homogeneous mixture or dispersion when HCBAs are used. One way of using HCBAs in conventional polyol mixtures can be to limit the amount of HCBA included in a polyol mixture to a low concentration, in order to avoid separation of the HCBA from the mixture. While separation of the HCBA can be avoided, the amount of blowing agent actually included in a polyurethane foam formulation can be an important factor in determining the quality of a polyurethane foam product. Having too low a concentration of blowing agent in a foam formulation can detrimentally affect the quality of a foam. For example, using too little blowing agent can cause the density of the foam to be too high. To prepare a low density foam, that is, a foam having a density of less than 2.5 lbs per cubic foot (pcf), it can be necessary to include more water than would otherwise be desirable when using conventional blowing agents. Increasing the amount of water in a foam formulation can detrimentally affect the 15 dimensional stability and long-term thermal conductivity of a foam due to the relatively fast rate of diffusion of carbon dioxide from a foam, compared with a hydrocarbon or halogenated hydrocarbon blowing agent.
HCBAs such as pentane and cyclopentane can be particularly incompatible with polyols substantially prepared using ethylene oxide and/or propylene oxide. Aromatic polyester polyols can incorporate only a limited amount of HCBAs. Surfactants can aid in making the components of a polyol mixture compatible, but are not completely helpful in making HCBAs compatible in a polyol mixture.
It would be desirable in the art of preparing polyurethane foams to utilize hydrocarbon blowing agents in a polyurethane foam formulation. It would also be desirable in the art of preparing polyurethane foams to make a low density foam from a polyurethane foam formulation that includes hydrocarbon blowing agents but does not require additional water in the formulation. Finally, it would be desirable in the art of preparing polyurethane foams to include hydrocarbon blowing agents in a foam formulation at a concentration that will yield a low density foam, wherein the hydrocarbon blowing agent does not phase separate from the formulation.